In response to the emissions reduction plea, governments of various countries have written policies to ban traditional incandescent lamps and advocate the use of compact fluorescent lamps (CFL). Despite the impending policies (such policies will be in effect as early as 2012), CFLs are already widely used due to their high lamp efficacy and long lamp lifetime. In comparison to incandescent lamps, CFLs only consumes one third as much electricity to have the same light output. In addition, CFLs create less heat (much of the incandescent lamp's energy is lost as heat) and their lamp lifetime can be up to ten times as longer. Therefore, since CFLs consume less energy and do not need to be replaced as often, they offer significant energy savings from both the utility and consumer standpoint in the long run.
The design of the electronic ballast circuit that drives a CFL is the major hurdle in the development of a high performance dimmable CFL. The electronic ballast is installed at the base of each CFL and it is used to perform essential lamp functions such as proper lamp ignition and lamp current stabilization. The majority of commercial CFLs (standard or dimmable) do not have any power factor correction (PFC) circuit. Without a PFC circuit, the ballast creates a highly distorted input current waveform because it draws current from the utility during the peak of the input AC voltage waveform for a relatively short period of time. Consequential to the distorted input current waveform drawn by the ballast, the CFL's power factor is quite low (typically 0.5 to 0.6). With regards to the performance of dimmable CFLs, its dimming range is very narrow when used in conjunction with standard phase-cut dimmers. Also, it has been noted that when the lamp is dimmed, flickering light output can be observed and in some cases, the lamp is unable to sustain normal operation.
The low power factor associated with CFLs are widely known, and have thus been addressed by using an electronic ballast that consists of a power factor correction (PFC) stage and a resonant inverter as shown in FIG. 1. This two stage ballast design is a typical solution to the power factor problem. The PFC stage allows the ballast circuit to draw a nearly sinusoidal line current at the input to achieve high input power factor. The resonant inverter, on the other hand, is responsible for the basic ballast functions (e.g. provide sufficient lamp ignition voltage across the lamp; stabilize the lamp current once the lamp is started; etc.). Although this two-stage configuration achieves high power factor at the input while performing the necessary ballast functions, it requires three active switches and a bulky, high voltage DC-link capacitor. As a result, the circuit is expensive and is quite bulky. In addition, since there are two power conversion stages, the efficiency of the circuit is also quite low.